Squeeze film damper seal

ABSTRACT

Shaft damper bearing utilizing spaced apart piston ring seals to seal off an annular squeeze film space between the rings, includes diagonal surface cross-section ring grooves in the bearing housing with diagonal cross-section rings in the housing grooves adapted to engage a bearing support undergoing radial motion in the housing.

BACKGROUND OF THE INVENTION

This invention relates to an improved squeeze film damper seal, and moreparticularly, to an improved piston ring seal and groove combinationwith adjustable piston ring sealing, for squeeze film dampers asassociated with high speed turbo machinery, for example, hot gas turbineengines such as aircraft gas turbine engines.

In a prior typical squeeze film shaft damper arrangement, a shaft withits associated rolling element bearing are permitted to have somelimited radial motion in the supporting bearing housing. Ordinarily anannular outer race of a supporting rolling element bearing of a shaftclosely fits in an annular chamber in the support housing where twoopposing closely adjacent circumferential surfaces of the housing andrace define a thin annular squeeze film space into which an oil underpressure is introduced for damping action on the race. The race isfitted with spaced apart concentric piston ring type seals whichcircumferentially engage the bearing housing to seal off the squeezefilm space between the rings. One problem with dampers as described, issealing of the fluid film squeeze film space by means of the describedpiston ring seals under the known variable operating conditions of thedamper. For example, the noted variable operating conditions includefluid pressure fluctuations adjacent the rings which lead to sealinginstability of the rings and excess damper fluid leaking withcompromised damper effectiveness. Furthermore, sealing ring and dampereffectiveness may not be constant for different levels of turbineoperation.

OBJECTS OF THE INVENTION

It is an object of this invention to provide improved piston ringsealing stability in a piston ring sealed squeeze film damper.

It is another object of this invention to provide an improved pistonring and groove combination and structure in a piston ring sealedsqueeze film damper.

It is a further object of this invention to provide an improvedadjustable sealing piston ring and groove arrangement for piston ringsealed squeeze film dampers.

SUMMARY OF THE INVENTION

An improved piston ring and groove arrangement for squeeze film damperscomprises a diagonal cross-section piston ring groove in a squeeze filmdamper housing with a diagonal cross-section and composite materialpiston ring in the housing groove and adapted to engage a bearingannular race to seal a squeeze film space between the race and thehousing. Mechanical adjustment means adjust ring to race sealing.

This invention will be better understood when taken in connection withthe following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial schematic and cross-sectional illustration of apiston ring sealed squeeze film damper.

FIG. 2 is a partial schematic and cross-sectional illustration of apertinent region of a piston ring sealed squeeze film space employingthe improved piston ring and groove arrangement and structure of thepresent invention.

FIG. 3 is a partial and schematic illustration of a tuning mechanism forthe improved piston ring and groove structure and arrangement of thisinvention.

FIG. 4 is a partial illustration of a maximum sealing position of thetuning mechanism of FIG. 3 as applied to the ring-groove sealcombination of this invention.

FIG. 5 is a partial and schematic illustration of the opposite extremeposition of the tuning mechanism of FIG. 3 as applied to the ring/grooveseal of this invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to FIG. 1, a squeeze film damper assembly 10 is combinedwith a rolling element bearing assembly 11 such as associated with highspeed turbo machinery, for example, hot gas turbine engines and aircraftgas turbine engines. Bearing assembly 11 comprises an annular inner race12 and a spaced outer annular race 13 with rolling elements 14therebetween. Inner race 12 is fitted on a rotor shaft 15 so that innerrace 12 rotates, with shaft 15, on rolling elements 14. A supportinghousing 16 for bearing assembly 11 includes an annular chamber 17therein, and outer race 13 is fitted or positioned in chamber 17 forlimited radial motion therein. The outer circumferential and planarsurface 18 of race 13 is closely adjacent an opposite circumferentialand planar surface 19 of housing 16 to define a thin annular squeezefilm space 20 therebetween. A damper fluid such as an oil underpressure, is introduced into squeeze film space 20 through anappropriate conduit or inlet 21 in housing 16.

Upon rotation of shaft 15, as a turbine rotor shaft, for example, anyshaft rotor imbalance may cause shaft 15 and, bearing assembly 11therewith, to undergo radial motion and subject oil in damper space 20to very high pressure to force viscous flow of the oil and a dampingaction on bearing assembly 11. In order to seal damper oil in squeezefilm space 20, race 13 includes a pair of spaced apart concentricgrooves 22 and 23 in its outer surface 18 with squeeze film spaced 20therebetween. A pair of metal gap piston rings 24 and 25 are fitted ingrooves 22 and 23 respectively and adapted to peripherally engagecircumferential wall 19 of chamber 17 to seal off squeeze film space 20.

In the arrangement as described, oil under pressure from squeeze filmspace 20 is utilized to assist ring and groove sealing. For example,each ring and groove combination is of a predetermined size to providean open narrow circumferential side vent space 26 as a part of eachgroove and circumferentially adjacent squeeze film space 20.Accordingly, each vent space 26, exaggerated for the purpose of clarityin FIG. 1, is in direct fluid flow relationship with squeeze film space20, and, as a result, high pressure in squeeze film space 20 istransmitted to vent space 26 where it is exerted against the adjacentside of a ring in its groove to urge the ring into firmer sealingrelationship with its opposite groove wall. However, favorable sealingeffects of vent spaces 26 are somewhat offset by a noted disadvantage. Avent space 26, having a fluid thickness significantly greater than thatof squeeze film space 20, comprises an unconstrained boundary forsqueeze film space 20, an arrangement which causes a concurrent decreasein squeeze film pressure axially along squeeze film space 20 approachingits boundary with a resultant loss of damper effectiveness. The improvedring and groove arrangement and structure of this invention obviates thedeleterious effect of a vent space 26 by the use of a particular ringand groove structure which does not require or utilize a vent space 26.Such an arrangement and structure is more clearly illustrated in FIG. 2where parts similar in design and function to those of FIG. 1 bear thesame numerals.

Referring now to FIG. 2, a squeeze film section 27 of a squeeze filmdamper includes a bearing race 13 cooperating with bearing housing 16 todefine a squeeze film space 20 which is bounded or sealed by spacedapart piston rings 28 and 29 of a diagonal (trapezoidal) cross-section.More particularly, piston rings 28 and 29 are metal-non-metal compositerings for better sealing effectiveness. For example, each ring 28 and 29includes an elastomer section 30 of a trapezoidal cross-section.Elastomer section 30 comprises three planar sides intersecting eachother at right angles. Two of the three sides are an opposite largerinner side and an outer shorter side. The inner and outer sides areconnected by a diagonal side in one direction and by the third or backside in the opposite direction. The trapezoid cross-section of elastomersection 30 is affixed to a right angle metal member 31 comprising a pairof planar sides in right angle relationship to each other. Asillustrated, the planar sides of metal angle member 31 are superimposedon or overlap the outer and back sides of elastomer section 30. However,the back side of elastomer section 30 is longer than the superimposedside of metal angle member 31 so that a part of elastomer section 30projects from metal angle member 31 as projection 32. It is onlyprojection 32 which engages race 13 with full surface contact withoutany metal to metal contact between angle 31 and race 13 within thelimitation of elastomer resiliency and the length of projection 32. Inthe present invention, piston ring grooves 33 and 34 are formed inbearing housing 16 so that the elastomer section 30 of rings 28 and 29radially and peripherally engage the circumferential surface 18 of race13 to seal squeeze film space 20 between rings 28 and 29. Moreover, eachring and its groove has a complementary diagonal cross-section where thediagonal surfaces of a ring and its groove are in spaced apartrelationship to define diagonal fluid filled spaces or zones 35 and 36having oil film thickness no greater than the thickness of the squeezefilm space 20 to which the zones are directly exposed in fluid flowrelationship. Other diagonal cross-sections may be utilized in thering-groove combination of this invention including triangular andsuitably modified polygonal and truncated geometrical figures, all ofwhich may provide a large slant or diagonal surface spaced from acorresponding groove surface to define high pressure oil filled diagonalzones 35 and 36. As illustrated in FIG. 2, the spaced apart pair ofdiagonal cross-section rings 28 and 29 are positioned in what may bedescribed as inverted truncated grooves to conform to the ringcross-sections in interfitting relationship, and so that the largerinner side or base of the trapezoid elastomer section 30 projects fromthe groove to peripherally engage surface 18 of race 13. Grooves 33 and34 project radially into circumferential wall 19 of housing 16 and theopposite ring diagonals, of the pair of rings 28 and 29, and walldiagonals, of the opposite grooves 33 and 34, are directed towards orface each other across squeeze film space 20, i.e. the ringcross-sections as shown in FIG. 2, are reversed one with respect to theother. Also, as illustrated in FIG. 2, squeeze film space 20 is borderedor bounded by rings 28 and 29 but the opposing housing and racestructures 16 and 13, respectively, axially extend to define furtherfilm spaces referred to as bumper portions of the damper.

Bumper portions 37 and 38 receive a supply of oil from leakage pastrings 28 and 29 and function as open end squeeze film damper segments.Oil leakage past rings 28 and 29 and from bumper portions 34 and 35 issubsequently collected for treatment, such as cooling, and recirculatedinto squeeze film space 20.

As illustrated, the vertical vent spaces or dams 26 of FIG. 1 are absentin FIG. 2, having been replaced with diagonal zones 35 and 36 which donot represent unconstrained boundaries for squeeze film space 20, andtherefore assist in maintaining a more constant and higher pressureaxially along squeeze film space 20. During operation of a damper ofthis invention, oil in diagonal zones 35 and 36 is uncavitated, andaccordingly hydrodynamic oil pressure in these zones bears on thediagonal surfaces of rings 28 and 29 to press the rings both laterallyand vertically for more effective sealing of the rings laterally withtheir groove wall, and peripherally with race 13. Replacement ofvertical spaces 26 with diagonal zones 35 and 36 represents what may bedescribed as an additional width effectiveness of squeeze film space 20without an actual increase in physical dimensions.

The improved piston ring seal of this invention may be provided with aninterrelated oil supply or delivery system which cooperates withdiagonal zones 35 and 36 of FIG. 2 not only for an improved oil supplybut also for use of the delivery oil for additional sealing of thepiston ring seals. Such an improved oil supply system is alsoillustrated in FIG. 2.

Referring again to FIG. 2 an oil supply system represented schematicallyas 39 includes a supply of damper oil under pressure and appropriateconduits leading to housing oil passages 40, 41 and 42, together withappropriate fluid flow controls to separately or selectively open andclose those conduits to the passage of damper oil therethrough. Oilpassage 40 leads directly to a central part of squeeze film space 20while passages 41 and 42 lead directly to diagonal fluid zones 35 and 36intermediate their ends where inlet oil is immediately brought to bearagainst the diagonal surfaces of the rings to press the rings laterallyagainst a groove wall and radially against race 13. The trapezoidalcross-section of rings 28 and 29 together with a correlation ofrespective groove, ring, and race diameters, advantageously providesfurther fluid filled ring spaces 43 between what may be described as theinner surface of a groove and the outer circumference of its fittedring. Spaces 43 are in fluid flow communication with squeeze film space20 through intermediate diagonal zones 35 and 36, and therefore transmitsqueeze film pressure to rings 28 and 29 for better radial sealingengagement with race 13.

In the oil supply system of this invention, inlet oil and inlet oilpressures are utilized to effectuate sealing of the damper during entryof the oil for efficient oil conservation. Three axially spaced oilinlet passages represent an advantageous oil delivery system for asqueeze film damper providing a measure of control over cavitation andoil pressure maintenance in the damper as well as reducing oil leakage.Preferably oil inlet passages 40, 41 and 42 each represent a pluralityof such passages spaced circumferentially about race 13 and rings 28 and29. Rings 28 and 29 are of the gap ring kind, i.e. in a circular orannular configuration with a gap space in the circle to define abuttingspaced apart ring ends or a gap. Such a gap provides compression andexpansion of the rings during damper operation under varying conditionswith continuous sealing while at the same time accommodating designtolerances in the damper structure. Metal angle 31 supplies structuralrigidity to a ring while at the same time permitting more of the volumeof the elastomer to engage in the resiliency of the structure.Resiliency of the ring structure of FIG. 2, together with the gapsupporting spring compression and expansion characteristics of angle 31,advantageously support a mechanical tuning or adjustment structure toprovide for a variation in sealing forces. Such an adjustment structure43 is illustrated in FIG. 3.

Referring now to FIG. 3, one composite diagonal ring such as ring 29 ofthe pair of rings 28 and 29 of FIG. 2 is illustrated in its operativeposition in a squeeze film damper with its diagonal zone 36 nextadjacent squeeze film space 20. An adjustment mechanism 44 is providedfor each ring, a description of one sufficing for the other. Mechanism44 comprises a screw 45 which passes through housing 16 to project intopiston ring trapezoidal groove 34 to bear against what may be describedas the top side of angle member 31. Screw 45 includes a threadedshoulder section 46 and a threaded shank section 47 which is threadedinto an appropriately threaded into an appropriately threaded aperturein housing 16. Housing 16 also includes a counterbore recess 48 at theentrance to the threaded aperture for screw 43. Shoulder section 46 ofscrew 45 joins shank section 47 at a rim or shoulder 49 which may bearagainst the bottom surface of counterbore 47 to limit progress of screw45 into housing 16 while at the same time limiting compression of ring29 as well as decrease of the ring gap space. Shoulder section 46 isalso threaded to receive a lock nut 50 thereon. Rotation of screw 45causes progression of screw 45 into housing 16 for the end of section 47to engage angle member 31 of ring 29 to bias ring 29 into firmerengagement with race 13 or, reversibly, to release compressive forcefrom ring 29. When the desired engagement is achieved, lock nut 50 maybe rotated to bear against housing 16 and frictionally bind screw 45 inthe desired position. Screw 45 is sealed against oil leakage by means ofa suitable washer or packing 51 in counterbore 48. The defined ring gapprovides a limit to the compressibility of the ring structure and isappropriately correlated to the ring groove diameter as well as to therace 13 diameter for proper sealing within the gap dimension.

Adjustment mechanism 43, as described, is utilized to adjust the ringgap to fit the noted ring groove and race 13 diameters. In thisconnection there are two extreme positions for adjustment as illustratedin FIGS. 4 and 5.

Referring now to FIG. 4, adjustment screws 45 have been rotated formaximum penetration into housing 16 and ring grooves 33 and 34. Thisposition represents a minimum value for the ring gap and ring internaldiameter for race 13, and maximum oil sealing. Also, maximum sealingincludes oil supply 39 (FIG. 2) being energized to open oil passage 41and 42 and close passage 40. Opposite conditions are shown in FIG. 5.

Referring now to FIG. 5, adjustment screws 45 are withdrawn a maximum sothat their end sections 46 permit some ring expansion away from race 13for controlled fluid leakage. In this position diagonal oil supplythrough passage 39 and 40 is closed off and ring gap and ring diameterare at their maximum value for the diameter of race 13. Ordinarily, anadjustment means 44 is employed for each ring. For more incrementaltuning or adjustment, a plurality of adjusting means 44 may be employedcircumferentially about the rings with oil supply passages such as 41and 42 located between pairs of adjustment means 44. The oil supplysystem of this invention with selective and controlled oil delivery ofmultiple circumferential passages at spaced plural axial locations,together with plural circumferential adjustment means, provides anextensive and wide range of adjustment of dynamic coefficients of thedamper. This result is accomplished with composite metal-non-metal gaprings with a screw mechanism sealing adjustment means.

The composite ring structure of this invention provides both a springeffect and radial flexibility. The spring effect of metal member 31 in agap ring with a screw 45 pressing on the ring is advantageous inproviding a certainty of a maximum gap for an installed ring I.D. Radialflexibility of the elastomer is necessary for proper circumferentialsealing when the elastomer is being compressed. Additionally the use ofa metal angle member 31 transmits the force of a usually small areascrew end to a much larger angle area for more uniform compression ofthe elastomer material section 30.

This invention provides improved fluid pressure activated piston ringseals in a squeeze film damper where diagonal cross-section rings havecomposite metal-non-metal parts and are fitted in corresponding diagonalcross-section grooves in a fixed bearing housing to seal against amoving bearing member. In one embodiment, the rings have a trapezoiddiagonal cross-section in which the non-metal part provides a sealingsurface against moving bearing member, and where mechanical tuning meansare utilized to adjust sealing engagement of the non-metal part.

While this invention has been disclosed and described with respect to apreferred embodiment thereof, it will be apparent to those skilled inthe art that various changes and modifications may be made withoutdeparting from the spirit and scope of the invention in the followingclaims.

What is claimed is:
 1. In a squeeze film shaft damper in which a rollingelement supported shaft has an annular bearing support fitted in anannular chamber in the bearing housing for limited radial motiontherein, and where the annular bearing support and an opposedcircumferential wall of said annular chamber of said housing define athin annular oil filled squeeze film space therebetween, the improvementcomprising(a) a pair of spaced apart concentric grooves in saidcircumferential wall of said housing with said squeeze film spacetherebetween, (b) said grooves having a diagonal cross-section, (c) apair of piston ring seals in said grooves, (d) said piston ring sealshaving a complementary diagonal cross-section to fit in said grooves ininterfitting relationship to define a diagonal zone between the groovediagonal and its ring diagonal, with the diagonal of said diagonalcross-section of each ring facing in a direction towards each other, (e)oil supply means connected to supply oil under pressure directly to thesaid diagonal zones between the groove diagonal and ring diagonal and(f) mechanical adjustment means in said housing to provide a compressiveforce on said rings to urge said rings into sealing engagement with saidbearing support.
 2. The invention as recited in claim 1 wherein said oilsupply is connected to said diagonal zones intermediate their ends. 3.The invention as recited in claim 1 wherein said oil supply is connectedto said diagonal zones at a plurality of circumferentially spacedlocations.
 4. The invention as recited in claim 1 wherein said diagonalcross-sections are trapezoidal cross-sections.
 5. The invention asrecited in claim 1 wherein said diagonal zones are in open fluid flowrelationship with said squeeze film space.
 6. The invention as recitedin claim 1 wherein said mechanical adjusting means comprises a screwthreaded into said housing to project into a ring groove and bearagainst the ring in said groove.